Because of the dramatic drop in cost of computer memory, it is becoming more economical and efficient to store film data in computer archival storage than in the film media itself. For example, in a large hospital hundreds of X-ray images are made every day. In the past these X-ray films were often stored indefinitely. It has been recognized that computer storage of such films is preferable if an image can be read and reconstructed with accuracy. Computer storage of such images is accomplished by laser writing and reading systems.
Laser writing and reading systems are known. For example, see U.S. Pat. No. 4,225,224 to N. Balasubramanian. Such systems commonly use photosensitive media for pre-recorded data being read or for writing new data. In either case, it is typical that a laser beam must rapidly scan the media, which is either reflective or transmissive of laser light.
The laser beam usually scans the medium by means of scanning optics, typically a scanning mirror or a rotating polygonal wheel having reflective surfaces. Such scanning is along a line extending across the width of the medium. To attain areawise media coverage, the medium is advanced relative to the beam, preferably in synchronism. Once a line has been scanned, the medium, usually film, is incrementally advanced a slight distance and an adjacent line is scanned. This is usually accomplished by mounting the film on a drum and rotating the drum by a slight amount after each line scan. Rotation is carried out by a stepper or other type of motor until the entire film has been scanned.
A problem with this approach is that the motor introduces a slight amount of vibration to the film, no matter how smooth the motor may be. This vibration causes film jitter which is seen on the film as lines, sometimes interfering with the ability to read data. In all cases it is easier to read data when there is no mechanical vibration of the film.
An object of the invention was to devise a means and method for reading and writing upon photosensitive media where the effects of vibration are substantially reduced.